how to install a cpu

I wanted to know what i need to upgrade my cpu. i have a mce 2005 with a AMD athlon 64 and i want to upgrade it to Athlon 64 x2 and i wanted to know if i need o update the bios or reinstall windows? Do i need a new heat sink and i new fan or can i use the same one being the same socket? what do i need to do to intall it and how to install the cpu? Thanks.

First thing you need to do is figure out if your motherboard will accept AMD x2 cpu's.
Mce 2005 is just media center, that has nothing to do with you getting a new cpu.
Find out what motherboard you have and we will help you find out what would be best for you.

You will want a new heatsink for the X2, however, one should come with the CPU if you buy it retail. As long as you get a CPU for the same socket (a 939 X2 if your current system is 939, an AM2 if your current system is AM2) you'll be fine, as far as I know all Athlon64 board support both the 64 and the X2. The one exception is socket 754, simply because there were no X2s made for socket 754.